1. Field of the Invention
This invention is related to a process of manufacturing thin ball grid array substrates and in particular to one which can provide a thin ball grid array substrate with thicker circuit lines without electroplating bus lines remaining.
2. Description of the Prior Art
Lightness, thinness and compactness are requisites for portable electronic devices, and so thin ball grid array substrates are widely used in these devices for achieving these purposes. The conventional process of manufacturing thin ball grid array falls into two categories, i.e. electrolytic electroplating and chemical electroplating.
The electrolytic electroplating process includes the following steps:
a. utilizing apolyimide film as a carrier 11; PA1 b. forming a thin copper layer 12 on the carrier 11 by sputtering; PA1 c. forming a thick copper 13 (which is thicker that the thin copper layer 12) on the thin copper layer 12 by flash plating; PA1 d. coating the top and bottom surfaces of the carrier 11 with a layer of photosensitive material 14; PA1 e. mounting a mask 15 with optically transmissible circuit track 151 on each of the top and bottom sides of the carrier 11, and then processing the carrier with exposure treatment; PA1 f. processing the carrier 11 with development treatment to remove the photosensitive material aligned to the circuit track 151 thereby forming a recessed electrical circuit track diagram; PA1 g. forming a copper layer 16 on the top surface of the carrier 11 by electroplating so that the copper layer 16 is coated on the copper layer 13 forming the recessed electrical circuit track with a top surface even with the photosensitive material layer 14; PA1 h. etching the bottom of the carrier 11 so as to remove the polyimide film aligned with the circuit track of the mask 15; PA1 i. washing away photosensitive material with chemicals; PA1 j. removing surplus copper layer 13 resulting in the circuit lines 19 and the electroplating bus lines 17 remaining (see FIG. 1l); and PA1 k. connecting electroplating bus lines 17 to positive and negative electrodes of an electroplating apparatus to coat a metal layer 18 of nickel, gold, or the like on the circuit lines 19.
Although the electrolytic electroplating process can provide thicker circuits and enables a manufacturer to select one of a number of metals to coat on the copper circuit, the electroplating bus lines 17 will remain, thereby often causing delay in high speed signal transmission, producing noise, and attenuating signal energy.
The chemical electroplating process can form an additional coating of nickel, gold, tin, or the like to cover the electroplating lines on the circuit, but the coating thickness is limited. Accordingly, there is no process which can provide a thick circuit without electroplating bus lines.
Therefore, it is an object of the present invention to provide a process of manufacturing thin ball grid array substrates.